Since the first successful demonstration of electricity generated from geothermal sources in 1904 in Larderllo, Italy (four lightbulbs were illuminated), the exploitation of renewable geothermal power (GTP) has continued to grow around the world. Currently more than 25 countries rely on some form of GTP for production of electricity, with the largest output coming from “The Geysers” in Santa Rosa Calif., USA. In an ideal situation, the subsurface fluid (4 km underground at greater than 100° C.) is pumped to the surface and the hot liquid is used to turn a steam turbine to generate electricity (i.e., a steam turbine system), returned underground by another well, geothermally re-heated, and the process started again. While GTP is a simple, cost effective, and ‘green’ method to produce self-reliant electricity, the number of acceptable, naturally occurring sites that can profitably generate electricity is limited. Therefore, interest has focused on using ‘hot rock’ sub-stratus to heat injected water (i.e., generate a heated aquifer). To maintain a ‘closed’ system, the rock between the two well bores must be explosively fractured. For both of these systems, the characterization of the reservoir fracture networks is important in the successful development GTP.
Often ion-based tracer studies are used to elucidate the extent and connectivity of these fracture networks. However, collecting real-time down-hole tracer data requires the development of novel ion detecting sensors. These detectors must survive the extreme brine pH levels (high and low), high temperature, high pressure, and other environmental conditions encountered in these deep-hole wells. Several detectors are being pursued for this application, including fluorine ion selective electrodes. One proposed material for the electrode is LaF3, which has shown some laboratory success. See N. I. Sorokin and B. P. Sobolev, Cryst. Reports, 842 (2007); and M. Bralic et al., Talanta, 581 (2001). However, a need remains for an improved method to synthesize LaF3 nanomaterials having increased detection capability.